A process for the preparation of a water-resistant boiled polyester powder coating

Abstract

The application discloses a preparation method of a water-resistant boiled polyester powder coating, which comprises the following steps: mixing carboxyl-terminated polyester resin as a film-forming material, a curing agent, a leveling agent, titanium white, and barium sulfate coated and modified by using an epoxy resin and benzoin, electrostatic spraying, and curing to obtain a film layer; wherein the powder particle size of the barium sulfate coated and modified by using the epoxy resin during mixing is D90≤20 mu m; the obtained film layer comprises barium sulfate particles coated by the epoxy resin, and the epoxy resin is subjected to ring-opening reaction with carboxyl groups of the polyester resin; the barium sulfate coated by the epoxy resin is uniformly dispersed by means of steric hindance of the epoxy resin during mixing, and the barium sulfate is also uniformly dispersed in the obtained film layer; the barium sulfate is effectively coated by the epoxy resin, the interface incompatibility between the barium sulfate and the polyester resin is effectively improved, the epoxy resin is used to participate in curing of the polyester resin, the obtained film layer is more compact, diffusion of water molecules in the film layer is difficult to be continuous, and weather resistance of the obtained film layer is significantly improved.

Description

[0001] This application is a divisional application of a patent application with the application date of May 31, 2023, the application number of 202310637001.6, and the invention name of a preparation method of a water-boiling-resistant polyester powder coating. TECHNICAL FIELD

[0002] The present application relates to the technical field of powder coatings, in particular to a preparation method of a water-boiling-resistant polyester powder coating. BACKGROUND

[0003] Powder coating is a new type of environmentally friendly coating that is different from oil-based coating and water-based coating. During coating, it does not use solvent or water as a dispersion medium, but uses air as a dispersion medium to uniformly coat the surface of a workpiece, and forms a coating film with special purposes after heating. Powder coating often uses electrostatic powder spraying, which uses high-voltage electric field induction effect to make the powder coating and the surface of the object to be sprayed have opposite electric charges, so that the powder coating is adsorbed on the surface of the object to be sprayed, and then solidified into a film.

[0004] The polyester used in powder coating is mostly carboxyl polyester resin or hydroxyl polyester resin, which needs to be matched with a curing agent, such as using E-12 epoxy resin in combination with carboxyl polyester resin. E-12 epoxy resin needs to use epichlorohydrin and sodium hydroxide as raw materials in preparation, so that E-12 epoxy resin contains a certain amount of sodium chloride and sodium hydroxide, which has a certain adverse effect on the water boiling resistance of the finally prepared powder coating. SUMMARY

[0005] The purpose of the present application is to provide a preparation method of a water-boiling-resistant polyester powder coating. The present application uses epoxy resin to modify precipitated barium sulfate, uses epoxy resin to effectively coat barium sulfate, effectively improves the interface incompatibility of barium sulfate and polyester resin, and simultaneously uses epoxy resin to participate in the curing of polyester resin, so that the obtained film layer is more dense, the diffusion of water molecules in the film layer is difficult to continue, and the weather resistance of the obtained film layer is significantly improved.

[0006] To solve this technical problem, the technical solution of the present application is as follows: a preparation method of a water-boiling-resistant polyester powder coating, mixing carboxyl polyester resin as a film-forming material, a curing agent for cross-linking reaction with the carboxyl polyester resin, a leveling agent, titanium white, barium sulfate modified by using epoxy resin coating, and benzoin, electrostatic spraying, and curing to obtain a film layer.

[0007] Preferably, the preparation method of the epoxy resin coated modified barium sulfate comprises the following steps:

[0008] S1, dispersing epoxy resin particles in barium chloride solution, wherein ethanolamine is dispersed in the barium chloride solution, heating to a temperature of 80-90°C, adding sodium sulfate solution under stirring to obtain barium sulfate precipitate with ethanolamine on the surface;

[0009] S2, filtering and washing the precipitate obtained in S1, and drying at low temperature;

[0010] S3, adding acetone to the barium sulfate-epoxy resin obtained in S2, wherein the epoxy resin is partially dissolved, and the barium sulfate with ethanolamine on the surface is connected to the epoxy resin through the amino group and ring opening, and the epoxy resin coats the barium sulfate;

[0011] S4, evaporating to remove acetone, and the epoxy resin is re-solidified due to the loss of acetone;

[0012] crushing and sieving to obtain epoxy resin-coated barium sulfate. The present application effectively improves the interfacial compatibility of barium sulfate and epoxy resin by using ethanolamine as a connecting material, and realizes the coating of barium sulfate by combining with the solubility characteristics of epoxy resin, and then forms a transition connection between epoxy resin and carboxyl polyester resin. The present application utilizes the hierarchical cooperation of barium sulfate-ethanolamine-epoxy resin-polyester resin to improve the dispersion of barium sulfate and establish stable dispersion and connection between barium sulfate and polyester resin. The obtained film layer is dense and the water resistance is significantly improved.

[0013] Preferably, the barium sulfate connected with ethanolamine is loaded on the surface of the epoxy resin particles. The present application effectively stirs the micro area formed by the crystal nucleus of barium sulfate precipitate by using epoxy resin particles. The crystal nucleus is branched with ethanolamine on the surface during precipitation. The amino group of ethanolamine effectively avoids the further continuation of hydrogen bonds, effectively improves the dispersibility of barium sulfate precipitate, and disperses around the epoxy resin particles during the formation of barium sulfate to form the loading dispersion of epoxy resin to barium sulfate.

[0014] Further improvement, the mass ratio of barium sulfate to epoxy resin is 1:(1-2). The amount of epoxy resin used in the present application is sufficient. First, the barium sulfate is on the surface of the epoxy resin, and then the barium sulfate is coated by using the solubility of the epoxy resin. The change of the relative position relationship between the two requires sufficient amount of epoxy resin; the coating of epoxy resin to barium sulfate effectively improves the possible agglomeration of nanoparticles during the mixing process, which leads to uneven dispersion of barium sulfate in the material, and the uniformity and consistency of the obtained film layer are good.

[0015] Further improvement, the mass ratio of ethanolamine to barium sulfate is 1:(10-20). The relative molecular mass of ethanolamine in the present application is small, and its influence on the viscosity of the solution system is small during the modification of barium sulfate, which is beneficial to the change of the relative movement speed of the epoxy resin particles relative to the solution system, thereby realizing the stirring of the micro area, promoting the uniform dispersion and modification of barium sulfate, and also facilitating the contact with the surface of the epoxy resin particles.

[0016] The mass of the epoxy resin to the volume of the acetone in S3 is preferably 1g:(20ml to 25ml). The present application uses acetone to dissolve the epoxy resin, and in the process of dissolution, the amino group of ethanolamine reacts with the epoxy group of the epoxy resin to achieve stable coating of the epoxy resin on the barium sulfate, with stirring.

[0017] The sodium dodecyl sulfate is preferably added in S1, and the mass ratio of the sodium dodecyl sulfate to the ethanolamine is (0.1 to 0.3):1. The present application adds the hydrophilic group of the sodium dodecyl sulfate to the barium sulfate solution, and the sulfate group is more easily combined with the BaSO4 particles, so that a coating layer is formed on the surface of the BaSO4, thereby changing the surface properties and effectively solving the problem of easy agglomeration of the BaSO4 during the drying process. At the same time, the good surface activity of the sodium dodecyl sulfate can reduce the surface tension of the solution and enhance the dispersibility of the solution, so that when the sodium sulfate is dropped into the barium chloride solution to form nuclei, it can be quickly dispersed to avoid the formation of too large barium sulfate crystals, and the micro-area stirring of the epoxy resin particles is also coordinated.

[0018] The mass of each component of the water-boiling-resistant polyester powder coating is preferably as follows:

[0019]

[0020]

[0021] The powder coating obtained by the present application effectively improves the interfacial compatibility between the barium sulfate and the polyester resin, and effectively improves the water-boiling resistance of the obtained film layer.

[0022] The above components of the powder coating are preferably mixed according to the mass ratio, extruded, tabletted, and broken by a double-screw extruder;

[0023] The tablet is crushed and sieved to obtain the powder coating;

[0024] The obtained powder coating is sprayed on the surface-treated tinplate substrate by an electrostatic spray gun, and is cured to obtain a coating layer.

[0025] The curing process conditions are preferably as follows:

[0026] The curing temperature is 175°C to 185°C, and the curing time is 15min to 20min.

[0027] The film layer water-boiling resistance test and evaluation method preferably includes the following steps:

[0028] S11, placing the film layer coated on the tinplate in normal-pressure boiling water and boiling for 2 to 4 hours; taking out and cooling and standing;

[0029] The film layer is obtained by spraying and curing the water-boiling-resistant polyester powder.

[0030] S12, test the color difference value of the film layer surface after S11, select one point as a reference point, and test the brightness difference value Delta l, red-green color difference Delta a and yellow-blue color difference Delta b of the remaining n-1 points and the reference point, and obtain the color difference value Delta E of the n-1 points, wherein

[0031]

[0032] The obtained Delta E is between 0.3 and 0.5 NBS; the water boiling resistance of the obtained film layer is conveniently judged by the color difference value, and the water resistance of the obtained film layer is good.

[0033] By adopting the above technical scheme, the present application has the following beneficial effects:

[0034] In the prior art, because sodium sulfate is dropped into barium chloride solution, a large number of nucleation occurs in the local space of the dropped barium chloride instantaneously, and the formed barium sulfate grains are large, while in the present application, the epoxy resin particles are first dispersed in the solution system, and with the stirring, the solid epoxy resin particles move in the solution relative to the liquid, thereby realizing the stirring of the micro area of the solution, wherein the instantaneously generated barium sulfate is impacted by the epoxy resin particles to avoid the growth of the barium sulfate grains; at the same time, the hydroxyl group of ethanolamine forms a hydrogen bond with the hydroxyl group on the surface of barium sulfate, and the amino group is weaker in polarity than the hydroxyl group, and it is difficult for the amino groups to form a hydrogen bond, so that the growth of the barium sulfate particles is effectively inhibited, and the combination of the hydroxyl group on the surface of the barium sulfate particles with water is also avoided, and the transformation of the hydroxyl group between the nano barium sulfate particles into an ether bond (-O-) during the drying process is avoided, thereby avoiding the agglomeration of the nano barium sulfate particles;

[0035] The present application utilizes the uniform dispersion of surface-modified barium sulfate and epoxy resin, utilizes the dissolution of epoxy resin in acetone, cooperates the ring-opening reaction of amino and epoxy under heating, ensures the stable connection of obtained barium sulfate to epoxy resin, further removes acetone, the re-coagulation of dissolved epoxy resin and the connection of barium sulfate to epoxy resin at the same time, forms the wrapping of barium sulfate, on the basis of the surface dispersion of barium sulfate modified by chain molecular structure of ethanolamine, further utilizes the chemical bond combination of epoxy resin to modified barium sulfate, further improves the poor interfacial compatibility of barium sulfate directly contacting with polyester resin by the further reaction of epoxy resin and polyester resin, the stable chemical bond connection of epoxy resin and barium sulfate through the hydroxyl and amino at both ends of ethanolamine, the reaction of epoxy resin and polyester resin, and the granular discontinuous distribution of epoxy resin in polyester resin; the small precipitation particle of barium sulfate modified by ethanolamine, long time stirring is needed to ensure the uniform mixing when mixing with other ingredients; the present application uses the wrapping of barium sulfate by epoxy resin, promotes the uniform dispersion of barium sulfate in raw materials by the uniform pre-dispersion of epoxy resin and the steric hindrance effect of epoxy resin, further densifies the film of barium sulfate and polyester resin under the wrapping of epoxy resin, effectively avoids the entry of water molecules into the film layer, forms the effective steric hindrance of hydrophilic barium sulfate in the film layer due to the wrapping of epoxy resin, avoids the initiation of film layer dissolution due to the existence of water molecules, and the obtained film layer has significantly improved water resistance, weather resistance and impact resistance.

[0036] The present application effectively wraps the hydrophilic barium sulfate, and the obtained film layer also has improved hydrophobicity. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 It is the preparation process flow chart of the epoxy resin wrapped modified barium sulfate in the present application;

[0038] Figure 2 It is the cross-sectional structure schematic diagram of the obtained film layer after the curing of the water-resistant polyester powder coating in the present application;

[0039] Figure 3 It is the structure schematic diagram of the epoxy resin wrapped modified barium sulfate particles in the present application;

[0040] Figure 4 It is the infrared spectrum diagram of the ethanolamine modified barium sulfate prepared by not using the micro-region stirring of epoxy resin particles in the comparative example of the present application.

[0041] In the figure:

[0042] Film layer 1; substrate 2; epoxy resin wrapped barium sulfate particles 3; epoxy resin 31; ethanolamine 32; barium sulfate 33. DETAILED DESCRIPTION

[0043] In order to further explain the technical solutions of the present application, the present application is described in detail below through specific examples.

[0044] Example 1

[0045] The present example discloses a preparation method of a water-resistant boiled polyester powder coating, a carboxyl polyester resin as a film-forming material, a curing agent which has a cross-linking reaction with the carboxyl polyester resin, a leveling agent, titanium white powder, barium sulfate coated and modified using an epoxy resin, and benzoin are mixed, electrostatic spraying, and a film layer is obtained by curing; wherein the powder particle size of the barium sulfate coated and modified using the epoxy resin during mixing is D90 of 17 μm; the obtained film layer includes barium sulfate particles coated with an epoxy resin, and the epoxy resin and the carboxyl group of the polyester resin form a stable interface by ring-opening reaction.

[0046] As shown in Figure 1 , the preparation method of the barium sulfate coated and modified using the epoxy resin of the present example includes the following steps:

[0047] S1, disperse the epoxy resin particles in a 0.5 mol / L barium chloride solution, wherein the barium chloride solution has ethanolamine dispersed therein, heat to a temperature of 80°C for the mixed system, and drop 0.5 mol / L sodium sulfate solution under stirring to obtain barium sulfate precipitate with ethanolamine connected to the surface;

[0048] S2, filter and wash the precipitate obtained in S1, and dry at low temperature;

[0049] S3, add acetone to the barium sulfate-epoxy resin obtained in S2, with the dissolution of the epoxy resin, heat to 75°C and stir, the barium sulfate with ethanolamine on the surface is connected to the epoxy resin by ring-opening connection of the amino group, and the barium sulfate is coated with the epoxy resin;

[0050] In the present example, the mass ratio of the epoxy resin to the volume of acetone in S3 is 1 g:20 ml.

[0051] S4, evaporate the acetone, and remove the solvent by vacuum drying the material after S3 for 4 hours at a temperature of 40°C, and the epoxy resin is again solidified due to the loss of acetone;

[0052] Pulverize and sieve to obtain the barium sulfate coated with the epoxy resin, as shown in Figure 3 .

[0053] In the present example, the mass ratio of the barium sulfate to the epoxy resin is 1:1.

[0054] In the present example, the mass ratio of the ethanolamine to the barium sulfate is 1:10.

[0055] The barium sulfate connected with ethanolamine in the embodiment is loaded on the surface of the epoxy resin particles, and the epoxy resin undergoes ring-opening reaction with the ethanolamine branched on the surface of the barium sulfate precipitate; the amount of the epoxy resin in the embodiment is obviously more than the amount of the ethanolamine, which sufficiently ensures that the ethanolamine serves as the connecting material of the barium sulfate and the epoxy resin, realizes the stable interface connection between the two, and also ensures that the epoxy resin has more residual epoxy groups, thereby ensuring that the epoxy resin fully reacts with the carboxyl polyester resin, and then forms a stable interlayer interface.

[0056] The acidity value of the carboxyl-terminated polyester resin in the embodiment is 32 mgKOH / g-38 mgKOH / g.

[0057] The epoxy resin in the embodiment is a solid bisphenol A type epoxy resin with an epoxy equivalent of 720 g / mol to 850 g / mol.

[0058] The above components of the powder coating in the embodiment are mixed according to the mass fractions recorded in Table 1, extruded, tabletted, and broken by a double-screw extruder;

[0059] The tablet is crushed and sieved to prepare the powder coating.

[0060] The obtained powder coating is sprayed on the surface-treated tinplate substrate by an electrostatic spray gun, and is cured to obtain a coating layer, as shown in Figure 2 , wherein the coating layer 1 is attached to the surface of the substrate 2, and the epoxy resin-coated barium sulfate particles 3 are uniformly dispersed in the coating layer 1, and further as shown in Figure 3 , the ethanolamine 32 connects the epoxy resin 31 and the barium sulfate 33.

[0061] The process conditions for curing in the embodiment are as follows:

[0062] The curing temperature is 180°C, and the curing time is 15 min.

[0063] Embodiment 2

[0064] The embodiment discloses a preparation method of a water-resistant boiling polyester powder coating. A carboxyl polyester resin as a film-forming material, a curing agent for cross-linking reaction with the carboxyl polyester resin, a leveling agent, titanium white, barium sulfate coated and modified by using an epoxy resin, and benzoin are mixed, electrostatically sprayed, and cured to obtain a film layer. The powder particle size of the barium sulfate coated and modified by using the epoxy resin in the mixing process is D90 of 18 μm. The obtained film layer includes barium sulfate particles coated by the epoxy resin, and the epoxy resin undergoes ring-opening reaction with the carboxyl of the polyester resin to form a stable interface.

[0065] As shown in Figure 1 , the preparation method of the epoxy resin-coated and modified barium sulfate in the embodiment includes the following steps:

[0066] S1, dispersing epoxy resin particles in 0.5 mol / L barium chloride solution, wherein ethanolamine is dispersed in the barium chloride solution, heating to 85℃ of the temperature of the mixed system, dropping 0.5 mol / L sodium sulfate solution under stirring to obtain barium sulfate precipitate with ethanolamine connected on the surface;

[0067] S2, filtering and washing the precipitate obtained in S1, drying at low temperature;

[0068] S3, adding acetone to the barium sulfate-epoxy resin obtained in S2, with the dissolution of epoxy resin, heating to 80℃ and stirring, the barium sulfate with ethanolamine on the surface is connected with epoxy resin through ring opening of amino group, and the epoxy resin coats the barium sulfate;

[0069] In this embodiment, the mass ratio of epoxy resin to acetone in S3 is 1g:25ml.

[0070] S4, evaporating to remove acetone, vacuum drying the material after S3 at 50℃ for 3 hours to remove solvent, and the epoxy resin is solidified again due to the loss of acetone;

[0071] Pulverizing and sieving to obtain epoxy resin coated barium sulfate, as shown in Figure 3 .

[0072] In this embodiment, the mass ratio of barium sulfate to epoxy resin is 1:2.

[0073] In this embodiment, the mass ratio of ethanolamine to barium sulfate is 1:20.

[0074] In this embodiment, the barium sulfate with ethanolamine connected on the surface is loaded on the surface of epoxy resin particles, and the epoxy resin reacts with the ethanolamine connected on the surface of barium sulfate precipitate; in this embodiment, the amount of epoxy resin is significantly more than that of ethanolamine, which fully ensures that ethanolamine serves as the connecting material between barium sulfate and epoxy resin, realizes stable interfacial connection between them, and also ensures that there are more epoxy groups remaining in the epoxy resin, so as to ensure that the epoxy resin fully reacts with the carboxyl polyester resin, and then forms a stable interlayer interface.

[0075] In this embodiment, the acidity value of the carboxyl-terminated polyester resin is 32mgKOH / g-38mgKOH / g;

[0076] In this embodiment, the epoxy resin is a solid bisphenol A type epoxy resin with an epoxy equivalent weight of 720g / mol to 850g / mol;

[0077] In this embodiment, the above components of the powder coating are mixed according to the mass fraction recorded in Table 1, extruded, tabletted, and broken by a double screw extruder;

[0078] The tablet material is pulverized and sieved to prepare a powder coating;

[0079] The obtained powder coating is sprayed on the surface-treated tinplate substrate by electrostatic spray gun, and is cured to obtain a coating layer, as shown in Figure 2 Figure 1, wherein the coating layer 1 is attached to the surface of the substrate 2, and the epoxy resin-coated barium sulfate particles 3 are uniformly dispersed in the coating layer 1, and further as shown in Figure 3 Figure 2, the ethanolamine 32 connects the epoxy resin 31 and the barium sulfate 33.

[0080] The process conditions for curing in this embodiment are as follows:

[0081] The curing temperature is 180°C, and the curing time is 15 min.

[0082] Example 3

[0083] The present embodiment discloses a preparation method of a water-resistant boiled polyester powder coating. A carboxyl polyester resin as a film-forming material, a curing agent for cross-linking reaction with the carboxyl polyester resin, a leveling agent, titanium white, and a barium sulfate modified by coating with an epoxy resin and benzoin are mixed, electrostatically sprayed, and cured to obtain a film layer; wherein the powder particle size of the barium sulfate modified by coating with an epoxy resin during mixing is D90 of 19 μm; the obtained film layer includes barium sulfate particles coated with an epoxy resin, and the epoxy resin is ring-opening reacted with the carboxyl group of the polyester resin to form a stable interface.

[0084] As shown in Figure 1 The preparation method of the barium sulfate modified by coating with an epoxy resin in the present embodiment includes the following steps:

[0085] S1, dispersing epoxy resin particles in a 0.5 mol / L barium chloride solution, wherein the barium chloride solution has ethanolamine dispersed therein, heating the mixed system to a temperature of 90°C, and adding a 0.5 mol / L sodium sulfate solution under stirring to obtain a barium sulfate precipitate having ethanolamine connected to the surface;

[0086] S2, filtering and washing the precipitate obtained in S1, and drying at low temperature;

[0087] S3, adding acetone to the barium sulfate-epoxy resin obtained in S2, and heating to 85°C with stirring, so that the barium sulfate having ethanolamine on the surface is connected to the epoxy resin through ring-opening of the amino group, and the barium sulfate is coated with the epoxy resin;

[0088] In the present embodiment, the mass / volume ratio of the epoxy resin to acetone in S3 is 1 g:20 ml.

[0089] S4, evaporating to remove the acetone, and vacuum drying the material obtained in S3 at a temperature of 60°C for 2 hours to remove the solvent, and the epoxy resin is again solidified due to the loss of acetone;

[0090] Pulverizing and sieving to obtain the barium sulfate coated with an epoxy resin, as shown in Figure 3 Figure 3.

[0091] The mass ratio of barium sulfate to epoxy resin in this embodiment is 1:1.

[0092] The mass ratio of ethanolamine to barium sulfate in this embodiment is 1:10.

[0093] In this embodiment, sodium dodecyl sulfate is also added in the step S1, and the mass ratio of sodium dodecyl sulfate to ethanolamine is 0.1:1.

[0094] In this embodiment, the barium sulfate connected with ethanolamine is loaded on the surface of the epoxy resin particles, and the epoxy resin reacts with the ethanolamine branched on the surface of the barium sulfate precipitate; in this embodiment, the amount of epoxy resin is significantly more than the amount of ethanolamine, which fully ensures that ethanolamine serves as the connecting material between barium sulfate and epoxy resin, realizes stable interfacial connection between the two, and also ensures that there are more epoxy groups remaining in the epoxy resin, thereby ensuring that the epoxy resin fully reacts with the carboxyl polyester resin, and then forming a stable interlayer interface.

[0095] The acidity value of the carboxyl-terminated polyester resin in this embodiment is 32 mgKOH / g-38 mgKOH / g;

[0096] The epoxy resin in this embodiment is a solid bisphenol A type epoxy resin, and the epoxy equivalent weight is 720 g / mol to 850 g / mol;

[0097] In this embodiment, the above components of the powder coating are mixed according to the mass fraction recorded in Table 1, extruded, tabletted, and broken by a double screw extruder;

[0098] The tablet is crushed and sieved to form a powder coating;

[0099] The obtained powder coating is sprayed on the surface-treated tinplate substrate using an electrostatic spray gun, and is cured to obtain a coating layer, as shown in Figure 2 , wherein the coating layer 1 is attached to the surface of the substrate 2, and the epoxy resin-coated barium sulfate particles 3 are uniformly dispersed in the coating layer 1, and further as shown in Figure 3 , the ethanolamine 32 connects the epoxy resin 31 and the barium sulfate 33.

[0100] The process conditions for curing in this embodiment are as follows:

[0101] The curing temperature is 180°C, and the curing time is 15 min.

[0102] Example 4

[0103] The present embodiment discloses a preparation method of a water-resistant boiled polyester powder coating, which comprises the following steps: mixing a carboxyl polyester resin as a film-forming material, a curing agent for cross-linking reaction with the carboxyl polyester resin, a leveling agent, titanium white, and barium sulfate coated and modified by using an epoxy resin, and benzoin, electrostatic spraying, and curing to obtain a film layer; wherein the powder particle size of the barium sulfate coated and modified by using the epoxy resin is D90 of 18 μm; and the obtained film layer comprises barium sulfate particles coated by the epoxy resin, and the epoxy resin is ring-opening reacted with the carboxyl of the polyester resin to form a stable interface.

[0104] As shown in Figure 1 The present embodiment discloses a preparation method of barium sulfate coated and modified by using an epoxy resin, which comprises the following steps:

[0105] S1, dispersing epoxy resin particles in a 0.5 mol / L barium chloride solution in which ethanolamine is dispersed, heating the mixed system to a temperature of 85°C, and adding a 0.5 mol / L sodium sulfate solution dropwise under stirring to obtain barium sulfate precipitate with ethanolamine connected to the surface;

[0106] S2, filtering and washing the obtained precipitate in S1, and drying at low temperature;

[0107] S3, adding acetone to the barium sulfate-epoxy resin obtained in S2, and heating to 80°C under stirring, so that the barium sulfate with ethanolamine on the surface is connected to the epoxy resin through ring-opening connection of the amino group, and the barium sulfate is coated by the epoxy resin;

[0108] In the present embodiment, the mass of the epoxy resin to the volume of the acetone in S3 is 1 g:25 ml.

[0109] S4, evaporating and removing the acetone, and performing vacuum drying on the material after S3 at a temperature of 50°C for 3 hours to remove the solvent, and the epoxy resin is again solidified due to the loss of acetone;

[0110] S5, crushing and sieving to obtain barium sulfate coated by the epoxy resin, as shown in Figure 3 .

[0111] In the present embodiment, the mass ratio of the barium sulfate to the epoxy resin is 1:1.

[0112] In the present embodiment, the mass ratio of the ethanolamine to the barium sulfate is 1:10.

[0113] In the present embodiment, sodium dodecyl sulfate is also added in the step S1, and the mass ratio of the sodium dodecyl sulfate to the ethanolamine is 0.3:1.

[0114] The barium sulfate connected with ethanolamine in the embodiment is loaded on the surface of the epoxy resin particles, and the epoxy resin undergoes ring-opening reaction with the ethanolamine branched on the surface of the barium sulfate precipitate; the amount of the epoxy resin in the embodiment is obviously more than the amount of the ethanolamine, which sufficiently ensures that the ethanolamine serves as the connecting material between the barium sulfate and the epoxy resin, realizes the stable interface connection between the two, and also ensures that the epoxy resin has more residual epoxy groups, so as to ensure that the epoxy resin fully reacts with the carboxyl polyester resin, and then forms a stable interlayer interface.

[0115] The acidity value of the carboxyl-terminated polyester resin in the embodiment is 32 mgKOH / g-38 mgKOH / g;

[0116] The epoxy resin in the embodiment is a solid bisphenol A type epoxy resin, and the epoxy equivalent weight is 720 g / mol to 850 g / mol;

[0117] The above components of the powder coating in the embodiment are mixed according to the mass fractions recorded in Table 1, and are extruded, tabletted, and broken by a double-screw extruder;

[0118] The tablet is crushed and sieved to prepare the powder coating;

[0119] The obtained powder coating is sprayed on the surface-treated tinplate substrate by using an electrostatic spray gun, and is cured to obtain a coating layer, as shown in Figure 2 , wherein the coating layer 1 is attached to the surface of the substrate 2 in the form of a film, and the epoxy resin-coated barium sulfate particles 3 are uniformly dispersed in the coating layer 1, and further as shown in Figure 3 , the ethanolamine 32 connects the epoxy resin 31 and the barium sulfate 33.

[0120] The process conditions for curing in the embodiment are as follows:

[0121] The curing temperature is 180°C, and the curing time is 15 min.

[0122] Table 1: Components and amounts (mass fractions) of the water-resistant polyester powder coatings in Examples 1 to 4

[0123]

[0124]

[0125] Comparative Example

[0126] The comparative example discloses a preparation method of a polyester powder coating. A carboxyl polyester resin as a film-forming material, a curing agent for cross-linking reaction with the carboxyl polyester resin, a leveling agent, titanium white, barium sulfate, and benzoin are mixed, electrostatically sprayed, and cured to obtain a film layer. The mass fractions of the above components are as follows:

[0127]

[0128] The solid bisphenol A type epoxy resin has an epoxy equivalent weight of 720 g / mol to 850 g / mol.

[0129] The method for modifying the dispersibility of barium sulfate with ethanolamine in the present comparative example comprises the following steps:

[0130] S1, ethanolamine is dispersed in a 0.5 mol / L barium chloride solution, heated to a temperature of 80°C for the mixed system, and 0.5 mol / L sodium sulfate solution is added dropwise under stirring to obtain barium sulfate precipitate with ethanolamine connected on the surface;

[0131] S2, the barium sulfate precipitate obtained in S1 is filtered and washed, and dried at low temperature;

[0132] The mass ratio of ethanolamine to barium sulfate in the present example is 1:10.

[0133] The acidity value of the carboxyl-terminated polyester resin in the present comparative example is 32 mgKOH / g to 38 mgKOH / g;

[0134] The epoxy resin in the present comparative example is the same as in examples 1 to 4.

[0135] The mass fractions of the above components of the powder coating are mixed in the present example, extruded, tabletted, and broken by a twin-screw extruder;

[0136] The tablet is crushed and sieved to prepare a powder coating;

[0137] The obtained powder coating is sprayed on a surface-treated tinplate substrate by an electrostatic spray gun, and cured to obtain a coating layer.

[0138] The process conditions for curing in the present comparative example are as follows:

[0139] The curing temperature is 180°C, and the curing time is 15 min.

[0140] The infrared spectrum of the ethanolamine-modified in-situ precipitated barium sulfate obtained in the present comparative example is shown in Figure 4 From Figure 4 it can be seen that 610 cm -1 , 983 cm -1 , and 1100 cm -1 are characteristic vibration peaks of barium sulfate, 3380 cm -1 is an absorption vibration peak of intermolecular hydrogen bond or O-H bond of water molecules in the sample, 1410 cm -1 is a bending vibration peak of OH-, and 1330 cm -1 is a characteristic absorption peak of C-N, which shows that the use of ethanolamine in the present application can effectively graft on the surface of barium sulfate precipitate.

[0141] The coatings obtained in Examples 1 to 4 and Comparative Examples were subjected to the following performance tests, and the thickness of the cured coatings was 120 ± 10 μm. The specific test data are shown in Tables 2 and 3.

[0142] 1. Impact performance

[0143] According to GB / T 1732-1993, the paint film was subjected to positive and reverse impact using a paint film impact tester, and the cracking of the paint film was observed.

[0144] 2. Gloss

[0145] According to GB / T 9754-2007, the 60° gloss of the coating was tested using a 60° gloss tester.

[0146] 3. Boiling water resistance

[0147] The film layer boiling water resistance test and evaluation method comprises the following steps:

[0148] S11. The film layer coated on the tinplate was boiled in normal pressure boiling water for 2 hours and 4 hours; and was taken out and cooled and placed;

[0149] S12. The color difference value of the film layer surface after S11 was tested. One point was selected as a reference point, and the brightness difference value Δl, the red-green color difference Δa and the yellow-blue color difference Δb of the remaining n-1 points and the reference point were tested, respectively, to obtain the color difference value ΔE of the n-1 points, wherein

[0150] The obtained ΔE was between 0.3 and 0.5 NBS.

[0151] 4. EIS test of the film layer

[0152] The electrochemical impedance test changes of the film layers obtained in Examples 1 to 4 and Comparative Examples before and after being immersed in deionized water for 24 hours were tested, and the value of low frequency impedance modulus (|Z|0.01Hz) represented the amount of water molecules entering the film layer.

[0153] 5. Static contact angle θ.

[0154] Table 2 Performance test indexes of the film layers obtained in Examples 1 to 4 and Comparative Examples

[0155]

[0156] Table 3 |Z|0.01Hz changes of the film layers obtained in Examples 1 to 4 and Comparative Examples before and after immersion

[0157] Item Soak 0 hours / (Ω*cm 2 ) Soak 24 hours / (Ω*cm 2 ​ Θ / ° Example 1 2.84*10 7 ]] 1.43*10 7 ]]> 120 Example 2 3.16*10 7 ]]> 1.52*10 7 ]]> 119 Example 3 3.08*10 7 ]]> 1.51*10 7 ]]> 121 Example 4 2.97*10 7 ]]> 1.50*10 7 ]]> 120 Comparative Example 2.88*10 7 ]]> 0.78*10 7 ]]> 106

[0158] It can be known from the data in Table 1, Table 2 and Table 3 that, in the application, the ethanolamine modified barium sulfate precipitate is first loaded by using the phase change of the epoxy resin, then the epoxy resin is dissolved from the solid phase to the liquid phase to react with the amino group of the ethanolamine to form the epoxy resin coated barium sulfate precipitate, and then the solvent is removed, the epoxy resin is solidified again to form positioning relative to the coated barium sulfate. Since the branching of the ethanolamine to the barium sulfate is formed by the surface hydrogen bond, the epoxy resin coated on the surface of the barium sulfate is also uniform. Therefore, with the synchronous mixing of the large particle epoxy resin, the barium sulfate is effectively dispersed in the coating by the steric hindrance of the peripheral epoxy resin, and is also uniformly dispersed in the coating after spraying and solidification. Since the barium sulfate-epoxy resin-terminated carboxyl polyester resin in the obtained film layer are connected by chemical bonds, the obtained film layer is more dense, and it is difficult for water molecules to enter and also difficult to form dissolution to the film forming material, so that the difference of the EIS test of the obtained film layer before and after soaking is small. At the same time, the barium sulfate is uniformly dispersed and stably connected with the polyester resin to form a connection, once the film layer is impacted or the diffusion of water molecules, the dense and continuous film layer effectively disperses the stress, the barium sulfate as a filler is uniformly dispersed, and the barium sulfate is connected to the polyester resin by the epoxy resin, so that the stress is dispersed when the film layer is impacted. When contacted with water, the hydrophobicity of the obtained film layer of the application is also significantly improved, and the dense film layer makes it difficult for water molecules to enter and form effective transmission, so that the film layer obtained by the application has good consistency, and the water boiling resistance and weather resistance of the film formed by the powder coating obtained by the application are improved. That is, from the data in Table 2 and Table 3, since the film layer is dense, the barium sulfate is more uniformly dispersed, and the interface connection is stable, the performance of the film layer of Examples 1 to 4 is significantly improved compared with the performance of the film layer obtained by the comparative examples.

Claims

1. A process for the preparation of a water-resistant boiled polyester powder coating characterized in that: Carboxyl polyester resin as film forming material, curing agent which has cross-linking reaction with carboxyl polyester resin, leveling agent, titanium white, barium sulfate coated with epoxy resin by modification and benzoin are mixed, electrostatic spraying, curing, to get film layer with barium sulfate-ethanolamine-epoxy resin-polyester resin layer cooperation, wherein the surface of barium sulfate with ethanolamine is coated with epoxy resin by amino ring opening connection, the epoxy resin and carboxyl polyester resin ring opening reaction to form stable interface; The preparation method of the barium sulfate coated with epoxy resin by modification comprises the following steps: S1, dispersing epoxy resin particles in barium chloride solution, wherein ethanolamine is dispersed in the barium chloride solution, heating to the temperature of the mixed system is 80-90℃, adding sodium sulfate solution under stirring to obtain barium sulfate precipitate with ethanolamine connected on the surface; the barium sulfate with ethanolamine connected is loaded on the surface of the epoxy resin particles; The mass ratio of barium sulfate to epoxy resin is 1: (1-2); The mass ratio of the ethanolamine to barium sulfate is 1: (10-20); S2, filtering and washing the precipitate obtained in S1, low temperature drying; S3, adding acetone to the barium sulfate-epoxy resin obtained in S2, heating and stirring with the dissolution of epoxy resin, the barium sulfate with ethanolamine on the surface is connected with epoxy resin by amino ring opening, and the barium sulfate is coated with epoxy resin; S4, evaporating to remove acetone, vacuum drying the material after S3 at a temperature of 40-60℃ for 2-4 hours to remove the solvent, and the epoxy resin is solidified again due to the loss of acetone; Pulverizing and sieving to obtain the barium sulfate coated with epoxy resin by modification.

2. The method of claim 1, wherein: The powder particle size of the barium sulfate coated with epoxy resin by modification during mixing is D90≤20μm. ​ 3. The production method according to claim 1, wherein: The mass of the epoxy resin to the volume of acetone in S3 is 1g: (20-25ml).

4. The production method according to claim 1, wherein: Sodium dodecyl sulfate is also added in S1, and the mass ratio of the sodium dodecyl sulfate to ethanolamine is (0.1-0.3):

1.

5. The production method according to claim 1, wherein: The mass fractions of the components of the water-resistant polyester powder coating are as follows: Carboxyl polyester resin 400-440 parts; Curing agent 80-100 parts; Leveling agent 16-20 parts; Titanium white 120-150 parts; Barium sulfate coated with epoxy resin by modification 140-170 parts; Benzoin 3-6 parts.

6. The preparation method according to claim 5, wherein: The above components of the powder coating are mixed according to the mass fractions, extruded, tabletted, and broken by a double screw extruder; The tablet is pulverized and sieved to obtain the powder coating; The obtained powder coating is sprayed on the surface treated tinplate substrate by an electrostatic spray gun, and cured to obtain the coating layer.

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